Water quality has become a matter of concern in recent years. Federal and State laws and regulations setting water quality standards have been adopted. These standards concern both suspended solids and dissolved matter; the latter is usually defined for regulator purposes as constituents which will pass through a 0.45 micrometer membrane filter. Large numbers of water samples have been collected from various sources and analyzed for the purpose of compliance with these standards. Some of these sources are in locations which are readily accessible to motor vehicles and machinery. Others can be reached only on foot.
The person collecting the water sample must decide whether to filter the sample in the field (i.e., at the site where the sample is collected) or simply to collect a sample and send it back to a laboratory for analysis. (On-site analyses are usually limited to a few determinations, such as temperature, pH, dissolved oxygen and specific conductance). A major advantage of filtration when suspended matter is to be studied is that the transport of large volumes of water can be avoided, since only the solids have to be sent back to the laboratory. Even when dissolved solids are of interest, an advantage of field filtration is that analytical results are usually more accurate if the sample is filtered in the field. This is pointed to, for example, in Brown, E; Skougstad, M. W. and Fishman, M. J., 1970, "Methods for Collection and Analysis of Water Samples for Dissolved Minerals and Gases", Techniques of Water Resources Investigations of The United States Geological Survey, Book 5, Chapter A1. This reference also described sampling methods and equipment to be used both when the sample is to be field-filtered and when it is not to be field-filtered. Whether or not the sample is field-filtered depends on the accessibility of the site and the equipment available.
Vehicle-mounted equipment (a gasoline engine-driven compressor, for example) can be used to separate suspended solids from water in accessible areas. Portable equipment is required in inaccessible areas. Such equipment includes, for example, a bicycle pump as disclosed in Brown et al., supra, page 16, another type of hand pump as disclosed in Siegel, F. R., Journal of Geological Education, 1985, vol. 33, pp. 132-133, or a battery powered portable peristaltic pump, also as disclosed in Siegel on page 132.
Each type of equipment described above has disadvantages which has limited its use. A peristaltic pump may be a Model WM-4-2w4 Sampler, made by Sigmamotor, Inc. of Middleport, New York and described in a brochure published by the manufacturer and in U.S. Pat. No. 2,818,815. The peristaltic pump can be used only for about 2 to 2.5 hours unless a battery recharger is available, according to Siegel. Siegel admits that his polypropylene hand pumps "are not made for extended use" and that their efficiency for vacuum filtration in the field diminishes after filtering 50 to 75 samples. The lack of any easily portable vacuum filtration equipment which can be used for filtering large numbers of samples in the field has limited studies on water sources in inaccessible areas and consequently has slowed compliance with water quality regulations.